linux-kernel - RE: [patch V2 38/38] x86/smpboot/64: Implement arch_cpuhp_init_parallel

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Message-ID: <87sfc92zw2.ffs@tglx>
Date:   Sat, 06 May 2023 18:22:37 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Brian Gerst <brgerst@...il.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Paul McKenney <paulmck@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Piotr Gorski <lucjan.lucjanov@...il.com>,
        Usama Arif <usama.arif@...edance.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        Mark Rutland <Mark.Rutland@....com>,
        Sabin Rapan <sabrapan@...zon.com>
Subject: RE: [patch V2 38/38] x86/smpboot/64: Implement
 arch_cpuhp_init_parallel_bringup() and enable it

On Sat, May 06 2023 at 00:53, Michael Kelley wrote:
> From: Thomas Gleixner <tglx@...utronix.de> Sent: Thursday, May 4, 2023 12:03 PM
> [snip]
>
>> @@ -934,10 +961,10 @@ static void announce_cpu(int cpu, int ap
>>  	if (!node_width)
>>  		node_width = num_digits(num_possible_nodes()) + 1; /* + '#' */
>> 
>> -	if (cpu == 1)
>> -		printk(KERN_INFO "x86: Booting SMP configuration:\n");
>> -
>>  	if (system_state < SYSTEM_RUNNING) {
>> +		if (num_online_cpus() == 1)
>
> Unfortunately, this new check doesn't work.  Here's the output I get:
>
> [    0.721384] smp: Bringing up secondary CPUs ...
> [    0.725359] smpboot: x86: Booting SMP configuration:
> [    0.729249] .... node  #0, CPUs:        #2
> [    0.729654] smpboot: x86: Booting SMP configuration:
> [    0.737247]       #4
>
> Evidently num_online_cpus() isn't updated until after all the primary
> siblings get started.

Duh. Where is that brown paperbag?

> When booting with cpuhp.parallel=0, the output is good.

Exactly that was on the command line when I quickly booted that change :(

The below should fix it for real.

Thanks,

        tglx
---
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -951,9 +951,9 @@ static int wakeup_secondary_cpu_via_init
 /* reduce the number of lines printed when booting a large cpu count system */
 static void announce_cpu(int cpu, int apicid)
 {
+	static int width, node_width, first = 1;
 	static int current_node = NUMA_NO_NODE;
 	int node = early_cpu_to_node(cpu);
-	static int width, node_width;
 
 	if (!width)
 		width = num_digits(num_possible_cpus()) + 1; /* + '#' sign */
@@ -962,7 +962,7 @@ static void announce_cpu(int cpu, int ap
 		node_width = num_digits(num_possible_nodes()) + 1; /* + '#' */
 
 	if (system_state < SYSTEM_RUNNING) {
-		if (num_online_cpus() == 1)
+		if (first)
 			pr_info("x86: Booting SMP configuration:\n");
 
 		if (node != current_node) {
@@ -975,11 +975,11 @@ static void announce_cpu(int cpu, int ap
 		}
 
 		/* Add padding for the BSP */
-		if (num_online_cpus() == 1)
+		if (first)
 			pr_cont("%*s", width + 1, " ");
+		first = 0;
 
 		pr_cont("%*s#%d", width - num_digits(cpu), " ", cpu);
-
 	} else
 		pr_info("Booting Node %d Processor %d APIC 0x%x\n",
 			node, cpu, apicid);